The ideal spectral profile of topical sunscreens.

Sunscreens were originally designed to prevent sunburn and incorporated active ingredients that absorbed principally in the UVB region. However, over the past 20 years or so new ingredients have been developed that extend absorption across a much wider range of the solar ultraviolet spectrum in the belief that sunscreens should provide balanced spectral absorption. This article develops the rationale for spectral uniformity by showing that this requirement is aligned to more natural forms of photoprotection. It is shown that a modern sunscreen can provide a spectrally balanced absorption profile in line with shade and many types of clothing fabric. Finally, a new metric is introduced that measures how well the spectral absorption profile of topical sunscreens performs against this ideal.